[Illustration: Fig. 29. A, _Trentepohlia umbrina_ Born.; B, _T. aurea_ Mart. × 300 (after Kütz.).] [Illustration: Fig. 30. Example of _Cladophora_. _Cl. glomerata_ Kütz. A, nat. size; B, × 85 (after West).] Fam. TRENTEPOHLIACEAE. Filamentous and branched, the filaments short and creeping or long and forming tufts and felts or cushions; colour, brownish-yellow or reddish-orange. TRENTEPOHLIA Born. Branching alternate; cells filled with red or orange oil; no pyrenoids (Fig. 29). A large number of lichens are associated with this genus: Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae, Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in part. Two species have been determined, _T. umbrina_ Born., the gonidium of the Graphidaceae, and _T. aurea_ which is associated with the only European _Coenogonium, C. ebeneum_ (Fig. 3). Deckenbach[287] claimed that he had proved by cultures that _T. umbrina_ was a growth stage of _T. aurea._ Fam. CLADOPHORACEAE. Filamentous, variously and copiously branched, the cells rather large and multinucleate. CLADOPHORA Kütz. Filaments branching, of one-cell rows, attached at the base; colour, bright or dark green; mostly aquatic and marine (Fig. 30). Only one lichen, _Racodium rupestre_, a member of the Coenogoniaceae, is associated with _Cladophora_. It is a British lichen, and is always sterile. Fam. MYCOIDEACEAE. Epiphytic algae consisting of thin discs which are composed of radiating filaments. 1. MYCOIDEA Cunningh. (Cephaleuros Kunze). In _Mycoidea parasitica_ the filaments of the disc are partly erect and partly decumbent, reddish to green (Fig. 31). It forms the gonidium of the parasitic lichen, _Strigula complanata_, which was studied by Marshall Ward in Ceylon[288]. Zahlbruckner gives _Phyllactidium_ as an alternative gonidium of Strigulaceae. 2. PHYCOPELTIS Millard. Disc a stratum one-cell thick, bearing seta, adnate to the lower surface of the leaf, yellow-green in colour. _Phycopeltis_ (Fig. 32) has been identified as the gonidium of _Strigula complanata_ in New Zealand and of _Mazosia_ (Chiodectonaceae), a leaf lichen from tropical America. [Illustration: Fig. 31. _Mycoidea parasitica_ Cunningh. much magnified (after Marshall Ward).] There is some confusion as to the genera of algae that form the gonidia of these epiphyllous lichens. _Phyllactidium_ given by Zahlbruckner as the gonidium of all the Strigulaceae (except _Strigula_ in part) is classified by de Toni[289] as probably synonymous with _Phycopeltis_ Millard, and as differing from _Mycoidea parasitica_ in the mode of growth. Fam. PRASIOLACEAE. Thallus filamentous, often expanded into broad sheets by the fusion of the filaments in one plane. PRASIOLA Ag. Thallus filamentous, of one-to many-cell rows, or widely expanded (Fig. 33). The gonidium of Mastoidiaceae (Pyrenocarpeae). [Illustration: Fig. 32. _Phycopeltis expansa_ Jenn. much magnified (after Vaughan Jennings).]